Identification, Expression, and Roles of the Cystine/Glutamate Antiporter in Ocular Tissues

Figure 2

Proposed roles of system x_c^-. Three main roles have been proposed for system x_c^-. (1) Excess cysteine is exported out of the cell via alanine-serine-cysteine transporter (ASCT) 1 and 2 or the system L amino acid transporter (LAT) 2 where it is oxidised to cystine and then taken up by xCT to maintain extracellular cysteine/cystine redox balance. (2) Cystine taken up by xCT is then reduced to cysteine, which is used for either GSH or protein synthesis. (3) Glutamate is transported out of the cell by xCT, which takes on added significance in neuronal tissues as it represents a nonvesicular route of release through which glutamate can potentially participate in neuronal signalling.